Problems wiith the notation

i have found a notation, which i never saw before and i can't give some reasonable definition for it.
Perhaps some of you guys have seen it before and can help me.

let [tex]k \in \mathbb{Z}^n[/tex] and N be a constant, what does [tex]<k>^N[/tex] mean?

I will put more of the context, where this appears:
Let P(x) be a polynomial of order m on [tex]\mathbb{R}^n[/tex]. For almost every [tex]\alpha \in A[/tex], there are constants C,N s.t.[tex] \left| P(k+\alpha)\right| \leq C<k>^N \forall k \in \mathbb{Z}^n[/tex].